Melting on the Greenland ice sheet is already happening at some of the fastest rates in centuries, and it’s only speeding up as the climate continues to warm. Now, a pair of new studies help explain why.
Rainfall is becoming increasingly common over parts of Greenland, one paper found, and it’s helping trigger sudden melting events that cause large amounts of ice to liquify and run off the edge of the ice sheet. Overall, the amount of melting associated with these events has doubled during the summer and more than tripled during the winter.
The other study found warming is moving the position of the snow line—the part of the ice sheet covered by snow—and exposing more bare ice to the atmosphere.
The two studies, both released this week, “are a really nice complement to each other,” according to ice expert Twila Moon of the National Snow and Ice Data Center, who was familiar with both.
The first demonstrates the way that rainfall can trigger melting events. Rain events may also affect the position of the snow line, which the second study demonstrates is another major factor in the rate at which the ice sheet melts.
“Both of them are saying, hey, we can already see how this is changing, and the really rapid climate change in just the last couple of decades is really playing out in how, where and how much melt we’re getting across the ice sheet,” Moon said.
In general, the total amount of precipitation falling on the Greenland ice sheet hasn’t changed, according to the first study; it’s just that in some areas, more seems to be falling in the form of rain, as opposed to snow. And it’s happening in both summer and winter, the research found.
The rainfall itself seems to be driven by cyclones that help carry warm, moist air over the ice sheet. To a certain extent, increases in these kinds of weather events may be linked to natural climate cycles.
But the recent changes—particularly the uptick in rainfall, as opposed to snow—are “unprecedented,” according to study co-author Marco Tedesco, a snow and ice expert at Columbia University.
Background warming is likely one factor at play. So are other more complicated changes in Arctic atmospheric circulation patterns linked to climate change. It’s thought that a variety of factors, from warming in the tropics to vanishing Arctic sea ice, may be playing a role.
“It’s important to understand that the atmosphere that is changing in the Arctic, that is really basically what’s feeding the changes in Greenland,” Tedesco said.
The type of precipitation that lands on the surface of the ice sheet can make a big difference in whether the sheet gains or loses mass.
When snow falls, it tends to accumulate on the surface, actually adding mass. Some scientists have suggested that parts of the Greenland ice sheet may actually see an increase in snow as the climate warms, which could help offset some of the melting.
On the other hand, rain tends to have the opposite effect. As it falls on top of the snow that’s already covering the ice sheet, rain starts to turn that snow into slush.
“Instead of a nice bright, white, fluffy snowflake, you have a wet, slushy snowball, and it wants to melt even more and absorb sunlight,” explained Luke Trusel, an ice sheet expert at Rowan University who commented on the new research for E&E News.
Even when it rains, some of the water may still refreeze and add mass to the ice sheet, the researchers noted. But in this case, they’ve found that the amount of runoff is so substantial that the increased melting is adding to the ice sheet’s overall decline.
The authors of the new study say rainstorms can also produce other feedback effects that help to temporarily enhance melting. Even as slushy snow starts to absorb more heat from the atmosphere, rain clouds can help trap that heat near the surface of the ice sheet, causing melting to proceed even faster.
The position of the snow line also has a major effect on surface melt, according to the other study released this week. As it retreats backward and leaves more ice uncovered, melting is expected to occur at faster and faster rates.
Trusel said that the basic process at play in the two studies is similar. In both cases, scientists are documenting a physical phenomenon that causes the ice sheet to absorb more sunlight and melt at faster rates.
In one case, it’s because rainfall is changing the consistency of the snow and allowing it to absorb more heat. In the other, the exposed ice tends to be darker in color than the bright, reflective snow, causing it to absorb more heat, as well.
Both are examples of effects that are “increasing the sensitivity of Greenland to continued warming,” Trusel said.
And as the climate continues to warm, both of these effects—rain-induced melting and snow line retreat—are expected to worsen, particularly in areas of southern Greenland, the studies suggest.
But even now, melting in Greenland is already occurring at record rates, according to scientists. A recent study from Trusel found the ice sheet is currently melting at its fastest rate in at least 350 years—and the melting seems to be speeding up (Climatewire, Dec. 6, 2018).
As Tedesco of Columbia University pointed out, some of the atmospheric changes affecting weather over the Greenland ice sheet are likely linked to climate change in other parts of the world.
At the same time, the melting of the Greenland ice sheet also has profound consequences for the rest of the planet: It can raise global sea levels and even affect the flow of major ocean currents.
In general, the rapidly warming Arctic—including, but not limited to, the Greenland ice sheet—is a prime example of the rippling effects of climate change around the world, noted Moon, who co-authored a commentary on the subject this week, as well.
“I just always really like to emphasize that these changes are not just some interesting natural phenomenon for us to watch,” she said. “They are really changes that we are taking a direct hand in creating, and we can take a really direct hand in influencing how much change we see into the future.”
Reprinted from Climatewire with permission from E&E News. E&E provides daily coverage of essential energy and environmental news at www.eenews.net.